Compositions containing cellulosic materials are made into particle boards, ceiling tiles, molded structures and the like. These compositions, however, are usually quite flammable because of the nature of the particles employed to prepare the composition. These cellulosic materials, for example, are wood, shell flour, cork as well as starch and other cellulosic waste products such as corncobs and rice wastes. These compositions are usually prepared by using these cellulosic materials to form commercial particle boards, ceiling tiles, and the like. The compositions are usually prepared by using urea/formaldehyde or phenol/formaldehyde resins as binders. These compositions, however, are flammable and for the most part the binders that are employed do not impart any non-flammable characteristics to the finished product. Therefore, it is often required that flame retardants be added. Although these flame retardants do in fact reduce the flammability characteristics of these materials, it is not sufficient to prevent the finished products from being considered essentially non-flammable. In addition, the use of flame retardants increases the cost of preparation of the various compositions.
We have found that certain urea/formaldehyde resins as described in U.S. Pat. No. 3,787,368 are excellent binders for reactive particles such as the cellulosic particles. The patent describes certain metal urea/formaldehyde resins as insloluble non-flammable polymers. We have found that these polymers not only act as excellent binders but also lead to compositions with reactive particles which are essentially non-flammable even though the particles from which they are made are indeed flammable. This is surprising since no mention is made in the above patent regarding the use of these polymers as binders, no less binders which would impart non-flammable characteristics to the finished composition. In addition, it is also surprising that these urea/formaldehyde resins impart non-flammable characteristics to the finished compositions, since other commercial binders such as PVC, phenol/formaldehyde and urea/formaldehyde resins which in themselves are also non-flammable do not impart non-flammable characteristics to compositions made therefrom. Further, compositions of this invention made from cellulosic materials and particularly wood and the urea/formaldehyde resins show a substantially higher oxygen index than do commercial compositions made from wood such as particle boards by Union Camp and U.S. Plywood. In addition, the tensile and flexural strength of the present compositions as well as nail and screw pull are generally comparable to commercial materials and in some compositions better than that found in the commercial wood compositions of various particle boards. The present compositions also have a very low swelling index, which is a significant feature because it is an indication that the composition is substantially water resistant.
It is therefore an object of this invention to prepare compositions from urea/formaldehyde resins and cellulosic materials, particularly wood, which are essentially non-flammable. Another object of this invention is to prepare compositions having good tensile and flexural strength, while still another object of this invention is to prepare cellulosic compositions which have a low swelling index. Yet another aspect of the invention, which is of substantial commercial value, is the ability to reduce press times for particle board manufacture from the present 5 to 11 minute cycle down to 1 to 5 minutes for boards 5/8" to 11/2" thick. Another particular aspect of this invention is the use of iron sulfate or preferably chloride waste products from the manufacture of TiO.sub.2 in the preparation of the resin. We have found that compositions forming excellent shaped articles can be prepared from these waste products which are substantially non-flammable and accordingly can help to eliminate an environmentsl waste disposal problem while forming a useful product.